The present invention relates in general to the separation of gases of differing molecular weights and, more particularly, to a gas separation method and apparatus utilizing a jet membrane.
Background art known to us consists of the following:
______________________________________ Reference No. Publications ______________________________________ (1) E. P. Muntz, B. B. Hamel and B. L. Maguire, AIAA J 1651, 8, 9, 1970. (2) J. Brook and B. B. Hamel, 7th Rarefied Gas Dynamics Symposium, Pisa, 1970. (3) E. P. Muntz and B. L. Maguire, 7th Rarefied Gas Dynamics Symposium, Pisa, 1970. (4) J. Brook, B. B. Hamel, E. P. Muntz, 8th Rarefied Gas Dynamics Symposium, Stanford, 1972. (5) P. A. Tahourdin. Final Report on the Jet Separation Methods, Oxford Rept. No. 36, Dr. 694, Claredon Lab., Oxford, England, 1946. (6) E. W. Becker and K. Bier, Z. Naturforsch, 9a 975-986, 1954. (7) E. W. Becker, K. Bier, H. Burghoff, O. Hagena, P. Lohse, R. Schutte, P. Turowski, and F. Zigan, Proc. U.N. Intern. Conf. Peaceful Uses At. Energy, 2nd Geneva, 1958 p/102 4, 455-457. (8) E. W. Becker, Proc. Intern. Symp. Isotope Separation, Amsterdam, 1957, 1958, 560-578. (9) E. W. Becker in H. London, ed., Separation of Isotopes, George Newness Ltd., London, 1961, Chap. 9. (10) P. C. Waterman and S. A. Stern, J Chem. Phys. 31, 405- 519, 1959. (11) V. H. Reis and J. B. Fenn, J Chem. Phys. 39, 3240-3250, 1063 (12) F. S. Sherman, Phys, Fluids 773, 8, 5, 1965. (13) R. Camparague, J Chem. Phys. 1795, 52, 4, 1970. (14) E. P. Muntz, B. B. Hamel and P. B. Scott, Entropie No. 42,1971. (15) G. Hertz Z. fur Physik 79, 109-121 (1932). (16) C. G. Maier, Mechanical Concentration of Gases - United States Department of the Interior, Bureau of Mines, Bulletin #431, 1940. ______________________________________ Reference No. U.S. PAT. No. Inventor(s) ______________________________________ (17) 2,607,439 Dickens et al (18) 3,279,155 Lambert (19) 3,320,722 Lucas (20) 3,362,131 Becker et al (21) 3,583,633 Campargue (22) 3,616,596 Campargue (23) British Pat. No. 794,834 ______________________________________
The jet membrane separation apparatus and process of the invention are based on different physical phenomena than other jet related separation schemes. However, since these schemes have some family relationship because of their use of jets, they are reviewed in this section. A technical description of the phenomena on which the jet membrane separation process depends is given in References 1 to 4 and 14.
The first report of separation in an expanding free jet was by Tahourdin (Reference 5) at Oxford, England in 1946. A mixture of gaseous species with disparate molecular weights was expanded through a nozzle into a region of low ambient pressure. The initial observation was that the heavier species was enriched along the centerline, while the lighter species was more abundant off-centerline. The effect was rediscovered by Becker (Reference 6) in 1954. Becker and his associates (References 7, 8 and 9) published a number of papers on this effect in the period of 1954 to 1963. In addition, Waterman and Stern (Reference 10) reported similar observations in 1959. The difficulty with these observations was that no theoretical model existed which could unify and explain the underlying mechanism. Also, certain of these experiments were performed with somewhat different configurations of nozzle and collector.
Between 1960 and 1965, the work of Fenn and associates (Reference 11) and Sherman (Reference 12) brought the earlier observations into clearer focus. Fenn, in a series of experiments, established that the observed separation phenomena was a collector or probe effect. An expanding mixture of gases showed very little actual separation. This conclusion was supported by the theoretical analysis of Sherman (Reference 12). Sherman utilized a hydrodynamic diffusion analysis to show that in the region of the expanding jet that could be described by continuum concepts, there was indeed very small separation. Further, unpublished work by one of the present investigators (Hamel) showed that in the non-continuum region of the flow, the thermal motion of the gas was so small that little off-centerline separation could be expected. By the late 1960's there was rather convincing evidence that little, if any, separation could be expected by expanding a gas mixture into vacuum. Some, but not remarkable, separations could be realized by making use of the probe separation effect (Reference 11). In addition, a definite separation could be obtained by the complex jet-skimmer configuration employed by Becker, the effect being associated with a centrifuging or turning of the jet rather than an expansion per se.
In 1970, Campargue (Reference 13) renewed interest in the problem by reporting a set of observations of large separation effects which resulted from the expansion of gas into a region -- not a vacuum -- but of low pressure. The really unusual aspect of this experiment was that Campargue put the gas mixture to be separated in the background gas, rather than in the expanding jet. Although Campargue's results represented a significant departure from all other work on free jet separation, there was no explanation for the underlying mechanism.
In discussions with Campargue in July, 1970, it became clear to us that the effect he was observing was attributable not to the structure of the expanding jet, but to the interaction between the background molecules and the expanding jet. In fact, we became convinced that an explanation of the results could be found in a series of papers, viz., Muntz, Hamel and Maguire (Reference 1); Brook and Hamel (Reference 2); Muntz and Maguire (Reference 3) published between 1968 and 1970, in which the foundations for the description of free jet-background interaction were presented. In the Fall of 1970, Muntz and Scott repeated Campargue's experiments at the University of Southern California, and additionally performed a set of experiments with other gases which showed that the separation effect was real, repeatable, and in fact probably even larger than reported by Campargue. These results and a simple theory were reported in the summer of 1971 by Muntz, Hamel and Scott (Reference 14)